S50 Line In low volume and sync issues

I have a S50 Pro+ and the ‘line in’ is connected to an Onkyo surround receiver TX-SR494 ‘line out’. This is a multi room set up with three A30+ in the system and when grouping them together the A30+ can only be heard if I turn the volume all the way up on each unit and the sound delay is about a second difference. Any advice on how to correct?